Leak proof bottom for a paperboard container

ABSTRACT

Disclosed is an improved bottom closure for a paperboard container of the type commonly used to package milk. The improvement specifically relates to the blank from which the container is formed. When a container is formed from a blank which embodies this improvement, leaks in the bottom closure thereof are substantially prevented.

United States Patent [191 Brownlee et al.

[ 1 LEAK PROOF BOTTOM FOR A PAPERBOARD CONTAINER [75] Inventors: Milton A. Brownlee; Robert L.

Lanham, both of Mobile, Ala.

[73] Assignee: International Paper Company, New

York, N.Y.

[22] Filed: July 12, 1973 [2]] Appl. No.: 378,491

[52] US. Cl. 229/38; 229/3.1; 229/43; 229/48 T [51] Int. Cl. B65D 5/08; B65D 5/40; B65D 5/62 [58] Field of Search 229/3.1, 17 G, 37 R, 38, 229/43, 44 R, 48 SC, 48 T [56] References Cited UNITED STATES PATENTS 2,362,862 11/1944 Sidebotham 229/48 T X 2,440,664 4/1948 lrons 229/48 T X 2,496,043 1/1950 Farrell 229/3.l UX

[ Oct. 21, 1975 2,926,777 3/1960 Maguire 229/37 R X 3,120,335 2/1964 Egleston et al. 229/17 G 3,194,473 7/1965 Rumberger 229/3.1 X 3,365,111 1/1968 McNair et al 229/17 G 3,412,922 11/1968 Miller et al. 229/17 G X 3,421,678 1/1969 Thompson et al. 229/3.1 3,455,496 7/1969 Franz 229/37 R 3,474,951 10/1969 Egleston et al. 229/17 G X Primary ExaminerJ0hn W. l-luckert Assistant ExaminerStuart S. Levy Attorney, Agent, or Firm-Alfred L. Michaelsen [57] ABSTRACT Disclosed is an improved bottom closure for a paperboard container of the type commonly used to package milk. The improvement specifically relates to the blank from which the container is formed. When a container is formed from a blank which embodies this improvement, leaks in the bottom closure thereof are substantially prevented.

16 Claims, 12 Drawing Figures US. Patent 0a. 21, 1975 Sheet 1 of6 3,913,825

US. Patent Oct. 21, 1975 Sheet 4 of 6 US. Patent 0a. 21, 1975 Sheet 5 of6 LEAK PROOF BOTTOM FOR A PAPERBOARD CONTAINER BACKGROUND OF THE INVENTION 1. Field to Which the Invention Pertains This invention pertains to the fluid packaging art.

A substantial quantity of fluids are packaged in paperboard containers which have been coated with a thermoplastic, e.g. polyethylene. Quantitatively, the major proportion of containers of this type are used for packaging milk. With respect to milk containers, the container construction which is predominantly used is a so-called gable top container which is formed from a one piece blank.

By way of background, milk carton blanks are typically manufactured by paper companies. More particularly, paperboard of the desired basis weight (pounds per three thousand square feet) is continuously manufactured on a paper machine and stored in large rolls. Subsequently, the paperboard thus manufactured is unrolled and fed through an extruder wherein polyethylene is extruded onto the surfaces of the paperboard to provide a coating. Thereafter, the thermoplastic coated paperboard is generally rerolled. The coated paperboard is fed into a press which cuts the continuous web of paperboard into the container blanks of the desired size. Additionally, the same press may be employed to provide appropriate score lines which facilitate the folding and erecting of the container as well as any printing or art work. Thus, the product resulting at this point is a flat, thermoplastic coated paperboard blank which has been appropriately cut and scored. Generally, at this point, the two longitudinal edges of the blank are joined so as to form a square tube. Commonly, the joining of the two longitudinal edges is achieved through a heat seal, i.e. the polyethylene coating adjacent to the two longitudinal edges is heat and the two heated edges are pressed together. Tubes of the type thus formed are generally sold in a flat condition, by the manufacturing company, to a dairy.

When received by the dairy, the paperboard tubes are usually sequentially fed into a so-called form, fill and seal machine. Typically, in such a machine, the paperboard tube which was shipped in a flat condition is formed into a square tube and deposited upon an upstanding, square mandrel. The tube is placed on the mandrel so that the part of the tube which will form the bottom of the container extends past the exposed end of the mandrel. Thereafter, the machine proceeds to position the carton under a heater which heats the polyethylene coating on the bottom forming flaps to a temperature at which the polyethylene coating will act as a bonding or adhesive agent. The machine then proceeds to manipulate the flaps extending past the end of the mandrel so as to form a bottom closure. When a bottom closure has been appropriately formed by juxtaposing the integral flaps on the tube, the mandrel moves such that a series of cooled plates (pressre pads) are pressed against the formed bottom for a time sufficient to effect a heat seal between the bottom forming flaps. Thereafter, the open top container thus formed is stripped off the mandrel, filled with milk and the top is appropriately sealed. For the purpose of describing the instant invention, the process steps of filling the container and sealing the top thereof are not particularly'significant because the instant invention relates to an improved, bottom closure.

What is of significance and what is thought to be apparent from the above description is the fact that, generally, the blanks used to form such containers are manufactured by paper companies while the blanks are formed into containers by dairies using large, expensive equipment which is located at the dairies. This duality is significant because attempts by a paper company to supply a superior container by altering the blank con-r figuration are thus constrained, i.e. a paper company cannot supply a blank which has been modified to the extent that the form, fill and seal machine will not accept it. Thus, any alteration made in the blank configuration must be such that it will not affect the ability of the machine to form a container from the blank.

In general, the problem of supplying blanks to a dairy for use in packaging milk has been resolved since a fully acceptable container blank for packaging milk has been designed and is known to the prior art. However, a very significant problem arises when a dairy elects to package and sell a liquid product other than milk. A similar problem arises when a company other than a dairy desires to use paperboard milk carton type containers to package liquids other than milk. The problems which arise under these circumstances are significant and often quite difficult to solve. The problem is significant because such companies can often achieve substantial economies if paperboard containers can be used. However, the difficulty arises because in order to achieve these economies form, fill and seal machines of the type used by dairies must be employed which, in turn again places a limitation upon the modifications which can be made by a paper company to the blank which they are supplying. In other words, the same container which is used to successfully package milk might not be successfully used to package other liquids. Examples of such other liquids, which may be referred to as penetrative liquids, are cooking oils and diet soft drink syrups. Liquids of this latter type, when packaged in milk carton type containers, frequently leak through the bottom closure of the container notwithstanding the fact that the same bottom closure and container may be used to successfully package milk. Indeed, an index of the difficulty of packaging liquids such as soft drink syrups is the fact that milk carton type containers are often provided with an interior metal foil laminate when such containers are used to package soft drink syrups. A container and container blank employing H such a construction is disclosed in US. Pat. No. 3,365,111 which is incorporated herein by reference.

The invention disclosed herein comprises the combination of a thermoplastic coated paperboard blank with an improved bottom closure. A blank embodying the instant invention may be formed into a container on a standard form, fill and seal machine which is either unmodified or only slightly modified depending upon the particular embodiment of the invention which is used. Moreover, the container resulting from erecting a blank which embodies this-invention (and which may also include an interior metal foil laminate) may be used to successfully package penetrative liquids such as soft drink diet syrups.

2. Prior Art Referring to the drawings, FIG. 1 shows the lower half of a paperboard blank of the type known to the prior art and which may be erected to form a container for packaging milk. The upper part of the blank 12 shown in FIG. 1 has been omitted since that part of the blank is known to the prior art and does not particularly pertain to the instant invention.

Referring to FIG. 1, it will be seen that the blank shown therein is comprised of two major portions, i.e. a body forming portion 13 and a bottom forming portion 14. The body forming portion 13 is comprised of four side wall panels 16, 17, 18 and 19, each having an equal width and forming the side walls of the erected container. The side walls 16, 17, 18 and 19 are connected by longitudinal fold lines 67, 78 and ,89 respectively. The bottom forming portion 14 is comprised of four flaps 16a, 17a, 18a and 19a. The aforementioned bottom forming flaps are connected to the side panels by transverse fold lines 26, 27, 28 and 29 respectively. Additionally, the four bottom flaps 16a, 17a, 18a and 19a are connected to each other by longitudinal fold lines 67, 78 and 89 respectively, i.e. the longitudinal fold lines which interconnect the bottom forming flaps are extensions of the fold lines which interconnect the side wall panels.

Generally, blanks of the type shown in FIG. 1 are provided with a so-called manufacturers joint which is'foldably connected to one of the side walls, e.g. 16. When the blank 12 is formed into a tube, the manufacturers joint is typically heated by an exposed flame and is then overlappingly bonded to the interir surface of the side wall panel 19 adjacent to its longitudinal edge 21.

Referring to bottom forming portion 14, it may be noted that certain of the bottom forming flaps which form this portion have a degree of symmetry. For example, referring to the bottom forming flaps 16a and 18a, which may be defined as gusset forming flaps, it may be noted that these flaps are spaced apart by the flap 17a but are otherwise symetrical. Thus, their transverse edges 46a, 46b and 48a, 48b are transversely aligned. Additionally, each of the gusset forming flaps is provided with two diagonally disposed score lines which define sub-panels. For example, referring to flap 16a, the diagonal score lines 31, 32 define sub-panels 16b, 16c and 16d. Similarly, diagonal score lines 33, 34 on the flap 18a define sub-panels 18b, 18c and 18d.

' Flap 19a may be referred to as a tuck-in flap and flap 17a may be referred to as a cover flap. It may be noted that in the prior art construction shown in FIG. 1, the transverse edge 49 of the tuck-in flap 19a and the transverse edge 47 of the cover flap 17a are substantially aligned.

When a blank of the type shown in FIG. 1 is to be erected to form a container, the blank is first formed into a tube as heretofore described. Thereafter, the gusset forming flaps 16a and 18a are urged downwardly into the container. As a result of this action, the triangular sub-panels 16b and 18b may be moved into a generally horizontal position. As a result of this action, the sub-panels 16c, 16d and 18c, 18d are folded back to horizontally overlie the sub-panels 16b, 18b respectively. Thus, a so-called gusset or triangular configuration is formed. The resulting triangular panels or gusset panels have an apex at the gusset points 40, 41.

Because all of the bottom forming flaps are foldably interconnected, the tuck-in flap 19a and the cover flap 17a will be moved into a horizontal position when the gusset forming flaps 16a, 180 are positioned as described above. More particularly, it may be noted that the longitudinal length of the tuck-in flap 19a and the cover flap 17a is greater than the longitudinal length of the gusset forming flaps. With regard to these dimensions, a number of factors should be pointed out. First, it may be noted that the adjacent transverse score lines are slightly displaced from each other. Thus, score lines 26, 28 are aligned with each other but are slightly longitudinally displaced from the aligned score lines 27, 29. This slight displacement of the longitudinal score lines is provided to insure that when the bottom is formed there is relatively no interference. Thus, the transverse score lines associated with the gusset forming flaps 16a, 18a are displaced slightly above the transverse score lines associated with the flaps 17a and 190 because the gusset forming flaps will be folded first and the flaps 17a and 19a will overlie the gusset forming flaps.

With further regard to the dimensions of the bottom forming flaps, it should be noted that containers of the type erected from a blank shown in FIG. 1 are generally square. Thus, the longitudinal height of the gusset forming flaps is generally equal to or slightly less than the width of the side wall panels so as to insure that when the gusset forming flaps are positioned within the container, the gusset points 40, 41 are almost touching.

Returning to a consideration of the manner in which the bottom forming portion of the blank 12 is erected, after the gusset forming flaps have been positioned horizontally within the container, the tuck-in flap 19a is horizontally positioned. Similarly, the cover flap 17a is also horizontally positioned so as to overlie the tuck-in flap 19a. Thus, it will be appreciated that the work tuck-in accurately describes the flap 190 since, when the bottom is formed, the edge 49 of the tuck-in flap 19a is, in fact, tucked in between the cover flap 17a and the sub-panels 16c, 16d and 18c, 18d.

Referring to FIg. 2, there is shown a view which illustratese a container bottom which would result from erecting the blank shown in FIG. 1. More particularly, the view shown in FIG. 2 is that which would appear if one viewed the resulting bottom closure looking down into the tube or open ended container. The resulting construction shown in FIG. 2 exemplifies the prior art and is representative of the bottom construction used on most paperboard milk cartons. Thus, it is instructive to consider this construction in some detail in order to obtain an understanding as to why this construction is deficient when one attempts to package certain liquids.

Considering the construction shown in FIG. 2, it may be noted that the gusset points 40, 41 disposed in the center of the container, are almost touching and define what might be referred to as a central axis. As previously indicated, the tuck-in flap 19a is disposed between the gusset forming flaps and the cover flap 17a. This is particularly evident in FIG. 2 where it may be noted that the edge 49 of the tuck-in flap 19a is clearly visible.

Another exposed edge which is clearly visible is the edge 20 associated with the manufacturers joint 15.

As previously indicated, when the gusset forming flaps 16a and 18a are folded into a horizontal position, their respective sub-panels 16c, 16d and 18c, 18d are folded back so as to form the gusset points 40, 41. As a result of this fold back action, the transverse edges associated with the gusset forming flaps are ultimately disposed in a channel forming relation. Thus, referring to FIG. 2, it may be seen that the transverse edges 46a and 46b associated with the gusset forming flap are disposed parallel to each other and underneath the gusset panel 16b. Similarly, the transverse edges 48a and 48b associated with the gusset forming flap 18a are disposed parallel to each other and underneath the gusset panel 18b.

Having described in considerable detail the prior art bottom configuration shown in FIG. 2, the deficiencies thereof and the manner in which these deficiencies arise may be clearly understood. Fundamentally, it has been discovered that all of these deficiencies are in the nature of leakage paths and appear to arise when there is a discontinuity between overlapping flaps or panels. Thus, it is believed that such discontinuities essentially form a channel through which leakage may occur. For example, referring to FIG. 2, when a bottom of the type shown therein is formed, a leakage channel is often simultaneously created along the exposed edge 49 of the tuck-in flap 19a. Liquid entrance of this leakage channel would occur at the intersection of the exposed edge 49 and the fold lines 32, 33. The manner in which this channel is formed may be appreciated by referring to FIG. 3 wherein the interrelation between various overlying panels and flaps is shown. Thus, in FIG. 3, it will be seen that the transverse edge of the tuck-in flap 1'9a causes a channel to form which is shown in cross section at 60 and may be referred to as the tuck-in flap channel.

Referring again to FIG. 2, the arrows 61 generally indicate paths of leakage along the exposed edge, 48a. The arrows 61 terminate at the edges of the container where the final leakage may occur. In an effort to block the leakage path formed by the exposed edge 49, the prior art has resorted to what are referred to as stakes. Briefly, stakes are indentations (22, 23 FIG. 2) formed in the bottom of container blanks perpendicularly across a leakage path. The stake or indentation is formed by providing a small, correspondingly shaped protuberance on the pressure pad on the form, fill and seal machine. The theory of staking is to provide, during the formation of the bottom, a zone which is subjected to high pressure and, thus, it is hoped the leakage channel will be blocked. While the use of stake points has been successful in preventing the leakage of milk, the same procedure has been relatively unsuccessful when attempts have been made to use milk car-- ton type containers to package liquids such as diet soft drink syrups.

Another leakage channel which is commonly formed and difficult to seal may be referred to as the gusset channel and is formed by the transverse edges of the gusset forming flaps. Thus, referring to the sectional view of FIG. 4, it may be seen that a gusset channel, shown in cross-section at 61, is formed between the two sub-panels 18d, 18c, the gusset panel 18b and the tuckin flap 19a. Entrance to the gusset channel is generally afforded at the gusset points 40, 41.

In general, attempts to package penetrative liquids in containers which have a bottom of the type shown in FIG. 2 have been unsuccessful because leakage occurred along either the channel 60 formed by the exposed edge 49 or the gusset channel 61 (the major leakage channels). As will hereinafter be described, the instant invention prevents leakage along these channels. Moreover, certain embodiments of the instant invention prevent leakage along two other channels which have been discovered (the minor leakage channels). Thus, referring to FIG. 2, it may be noted that the gusset forming flap 16a overlies the bottom portion of the manufacturers joint 15. As a result, it has been discovered that a leakage channel may exist adjacent to the edge 20 of the manufacturers joint 15. This leakage channel (which may be referred to as the side seam leakage channel) arises in essentially the same manner as the leakage channel associated with the exposed edge 49 of the tuck-in flap 19a, i.e. the exposed edge which is sandwiched between the other panels causes a channel to be formed adjacent thereto. Once again, the prior art has attempted to seal this leakage channel by resorting to the use of stake points, e.g. stake point 24 as shown in FIG. 2.

Other leakage channels which have been identified are formed at the fold lines which connect the gusset flaps to the cover flap 17a and the tuck-in flap 19a. For example, one of these channels is clearly shown in FIG. 5 wherein the channel is shown, in cross section, at 65. Entrance to this channel is at the corner of the container as shown by the arrow 64 and the subsequent arrows which follow the path of the channel. As shown in FIG. 5, the fold line associated with the channel 65 (which may be called a corner channel) is fold line 67. A total of four such corner channels may be formed, i.e. one such channel associated with each of the fold lines 56, 67, 78 and 89.

Although prior art has recognized the need to provide a leak proof bottom an effective and economical solution to this problem has not heretofore been found when such containers are used to package penetrative liquids such as diet soft drink syrup. The art has attempted to provide a leakproof bottom by overcoating the entire bottom of the container. For example, one such prior art approach contemplates spraying the entire bottom interior of a carton with wax or a thermoplastic material after it is erected. Of course, such an approach requires a substantial addition to and modification of the forming machine and, additionally, consumes a considerable quantity of coating material. US. Pat. No. 3,365,111 discloses such a formed container wherein the bottom exterior is overcoated with a film. A similar overcoating, in the nature of an increased coating of the bottom panels, is disclosed in US. Pat. No. 3,421,678. Apparently, the prior art resorted to the overcoating approach because of the assumed difficulty or impossibility of selectively applying a bead or globule of thermoplastic coating material at the prime location of the leak forming creases described in US. Pat. No. 3,421,678.

In summary, the leakage channels, both major and minor, associated with a bottom closure of the type most commonly used by the prior art have been described. The invention disclosed herein and hereinafter described seals the major leakage channels described above. Additionally, certain embodiments of the instant invention function to seal all of the channels previously described.

SUMMARY OF THE INVENTION In combination with a thermoplastic coated paperboard blank of the type commonly used to form milk containers, an improved bottom forming portion is provided. In accordance with the improvement, a narrow band or bead of thermoplastic material is disposed upon the interior side of at least one of the bottom forming flaps so as to extend outwardly from the gusset points and along the gusset channel when a container is formed from the blank. Preferably, a band or bead of thermoplastic material is disposed upon at least the center portion of each of the bottom forming flaps and the beads are substantially aligned and the beads on the gusset forming flaps are adjacent to the exposed edges thereof.

At least the center portion of the transverse edge of the tuck-in flap is substantially aligned with the transverse edges of the gusset forming panels and the remainder of the edges of the tuck-in flap are disposed to underlie the gusset forming flaps when said blank is erected.

The thermoplastic material preferably has a melt index in the range of 3.0 to 300.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a paperboard blank known to the prior art.

FIG. 2 is a plan view of a container bottom of the type resulting from erecting the blank of FIG. 1.

FIG. 3 is a fragmentary, sectional view taken along the section lines 33 of FIG. 2.

FIG. 4 is a fragmentary, sectional view taken along the section lines 44 of FIG. 2.

FIG. 5 is a fragmentary, sectional view taken along the section lines 55 of FIG. 2.

FIG. 6 is a view illustrating a preferred embodiment of my invention.

FIG. 7 is a plan view of a container bottom of the type resulting from erecting the blank of FIG. 6.

FIG. 8 is a fragmentary, sectional view taken along the section lines 88 of FIG. 7.

FIG. 9 is a fragmentary, sectional view taken along the section lines 88 of FIG. 7.

FIG. 10 is a view illustrating another embodiment of my invention.

FIGS. 11 and 12 are plan views of a container bottom and illustrate a structural requirement of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 6, a paperboard blank 12 is shown and represents a preferred embodiment of the instant invention. As may be noted, a major portion of the blank 12 shown in FIG. 6 is substantially identical to the blank 12' of FIG. 1. Thus, to the extent that these two blanks are the same, the same reference numbers have been employed.

The first structural difference between the blank 12 in FIG. 6 and the blank 12 of FIG. 1 comprises the cutout 80 in the tuck-in flap 19a. The purpose of the notch or cut-out 80 is to alter the structure of the tuck-in flap 19a such that at least the center portion of the transverse edge thereof is aligned with the transverse edge of the gusset forming flaps 16a and 18 a. Thus, it will be seen that there is provided a transverse edge 81 which is centrally located on the flap 19a and aligned with the transverse edges 46a, 46b and 48a, 48b of the gusset forming flaps.

The second structural difference between the prior art blank shown in FIG. 1 and the embodiment of this invention shown in FIG. 6 relates to the addition of a narrow band of thermoplastic material 92 which is disposed adjacent to the transverse edges of the flaps 16a and 18a on the interior side thereof and extends across the entire width of the blank 12.

Referring to FIGS. 7, 8 and 9, there is shown therein views of the bottom closure which results when the blank 12' of FIG. 6 is erected. Referring to FIG. 7, there is shown a view of the resulting bottom structure as it would appear when viewed from within the container and prior to the heat sealing step. Initially, it may be noted that the cutting of the tuck-in flap as hereinbefore described has the effect, when the blank is formed into a container, of aligning the edge 81 with the gusset points. As such, the tuck-in flap channels and the gusset channels are substantially coincident in the region that the band of adhesive 92 is visible between the gusset points. Also, because of the manner in which such containers are erected, the transverse edges of the gusset forming flaps are placed adjacent to one another and, thus, the adhesive band 92 which is disposed adjacent to these transverse edges is now in the form of two adjacent bands underneath the subpanels 166, 186. This configuration can be seen more clearly in the sectional view FIGv 8 which shows the inter-relation of the various bottom forming flaps prior to heat sealing. Thus, in FIG. 8, the combined gusset channel and tuck-in flap channel 60 is clearly evident and, additionally, the juxtaposition of the various portions of the adhesive band 92 is also evident.

The utility of providing an adhesive band 92, as previously described, is particularly apparent by considering and comparing FIG. 8 and FIG. 9 wherein FIG. 9 illustrates the same section shown in FIG. 8 except, unlike the view of FIG. 8, the view of FIG. 9 corresponds to how this section would appear after the heat sealing step. Thus, it will be seen that during the heat sealing step, the thermoplastic band 92 has been melted and, as a result of the pressure applied to the bottom of the container, the melted thermoplastic substantially fills the channel 60. Additionally, returning to a consideration of FIG. 7, it will also be appreciated that when the bottom shown therein is subject to a heat sealing step, the portion of the thermoplastic band 92 which is visible in FIG. 7 will also be melted and, as a result, the gusset points are sealed and the exposed edge of the tuck-in flap 19a is sealed. Thus, the major leakage channels as well as the entrances thereto are automatically sealed when a blank of the type shown in FIG. 6 is erected and sealed.

Additionally, referring again to FIG. 7, it may be noted that the juxtaposed thermoplastic band 92 extends across the width of the container from the side wall 16 to the side wall 18. This alignment of the thermoplastic band 92 such that portions thereof are adjacent to the side walls 16 and 19 is significant because, as a result, when the bottom closure is heat sealed, the so called comer leakage channels and the side seam leakage channel are sealed. That is to say, referring back to FIG. 2, it will be seen that the leakage path 63 associated with the side seam channel and the leakage path 64 associated with the comer leakage channels both terminate at the intersection of the side wall 16 with the adjacent gusset channel formed by the edges 46a and 46b. Thus, since the thermoplastic band 92 is overlapped or juxtaposed at this point, when the bottom is heat sealed the termination of the leakage path 63 and the leakage path 64 is also sealed. Therefore, it will be appreciated that the blank construction shown in FIG. 6 effectively seals all of the leakage channels which have been discovered.

Considering again the blank shown in FIG. 6, a number of advantages attend the use of this embodiment of the invention, i.e. this embodiment of the invention is particularly desirable from a manufacturing point of view. For example, since the thermoplastic band 92 is a continuous band, the machines which form the blank from the thermoplastic coated paper roll stock may easily be adapted to continuously deposit the required thermoplastic band. Indeed, it has been surprisingly discovered that the adhesive band 92 may be deposited upon the blank before the blank is appropriately scored, i.e. it has been surprisingly determined that the adhesive band 92 does not interfere with the scoring operation.

With respect to the continuous nature of the thermoplastic band 92, it has been found that an acceptable bottom closure may be formed if the narrow thermoplastic band is deposited only upon the center portion of the bottom forming flaps. Such a construction, which is shown in FIG. 10, will seal the major leakage channels but will not seal the minor leakage channels because there will not be any thermoplastic material adjacent to the side walls 16 and 18 when the blank is erected. Thus, the bands 93, 94, 95 and 96 will seal the major leakage channels when the blank of FIG. is erected and heat sealed.

With regard to the thermoplastic band described above, the thermoplastic material selected must meet certain criteria. For example, the material which comprises the thermoplastic band must be such that it will, upon melting and rehardening, adhere to the thermoplastic coating on the paperboard blank. Since the vast majority of such paperboard blanks are coated with polyethylene, the thermoplastic material must satisfy this requirement with respect to polyethylene. Another requirement which such thermoplastic material must satisfy relates to the so-called melt index. Essentially, the melt index is a measure of the flowability or viscosity of a thermoplastic at an elevated temperature. In order for a thermoplastic material to perform satisfactorily, the thermoplastic must have a degree of flowability at the heat seal temperatures which are encounterd in order to insure that the heated thermoplastic material will seal the leakage channels. However, the viscosity of the heated thermoplastic cannot be so low that the heated thermoplastic will be unduly dissipated by flowing over too large an area. Experiments conducted upon the occasion of this invention have determined that a thermoplastic with a melt index in the range of, approximately, 3.0 to 300 is acceptable.

Returning to a consideration of the blank shown in FIG. 6, and particularly the cut-out or notch in the tuck-in flap 19a which forms the aligned transverse edge 81, it may be noted that the remainder of the exposed edges of the flap 19a extend longitudinally beyond the edge 81. This longitudinal extension of the remainder portion of the flap 19a is preferable because the portions of the flap 19a which extend beyond the edge 81 cooperate with the remainder of the flaps during erection of the blank in a manner which facilitates the forming of the bottom portion of the container. Although it is preferable to utilize a'tuck-in flap wherein the side portions extend beyond the transverse edge 81, the edges of the remainder portion of the tuck-in'flap must be disposed so as to underlie the gusset forming flaps when the blank is erected. This latter requirement, i.e. that the remainder of the edges underlie the gusset forming flaps when the blank is erected, is important in order to insure that the only entrances to the tuck-in flap channel are adjacent to and substantially aligned with the gusset points. Thus, the edges of the tuck-in flap may be disposed as shown in FIG. 11 but not as shown in FIG. 12 wherein the remainder of the edges of the tuck-in flap do not all underlie the gusset flaps, e.g. as at 101 and 102. An acceptable alternative construction would be to transversely cut the entire tuck-in flap so that the exposed edge thereof was aligned with the gusset flaps as suggested by the dotted line representation 108,109 in FIG. 10.

With further regard to the cut-out in the flap 19a which forms the transversely aligned edge 81, it should also be noted that, in the embodiment of FIG. 10, the length of the narrow thermoplastic bands of material must be at least equal to the length of the aligned transverse edge 81. Such a minimum length is necessary in order to insure that the gusset points and the entrances to the tuck-in flap channels are effectively sealed as shown in FIG. 9.

With regard to the width of the narrow thermoplastic band or bands, the preferable minimum width of each band should be approximately 0.125 inches but preferably not greater than, approximatley, 0.5 inches. A width greater than 0.5 inches is economically disadvantageous. In any event, the width of the beads should not be greater than the longitudinal length of the bottom closing flaps. The minimum length of the discontinuous bands of thermoplastic will depend upon the particular construction employed with respect to the tuck-in flap and the size of the container. Suffice it to say, therefore, that depending upon these factors, a minimum length will be selected which is at least sufficient to effect a sealing of the gusset points and the entrances to the tuck-in flap channel. As an example, in a one gallon container, if the rectangular notch construction of FIg. 6 is employed, the notch should be at least, approxi mately, 0.5 inches wide and the bands of discontinuous thermoplastic should preferably be at least 0.5 inches long. Preferably, the thermoplastic material employed is a hot melt adhesive having a melt index in the range previously stated. An acceptable hot melt is sold by Stein Hall Company under the designation LHM 597.

Considering the thickness of the thermoplastic bead, the minimum thickness for achieving a sealing of the various channels using the embodiments of the invention heretofore described is 5 mils. Preferably, a thickness of approximately 10 to 12 mils is employed.

Reflecting upon the embodiments of the invention heretofore disclosed, it may be noted that an intrinsic advantage of these embodiments is the fact that they not only seal the major leakage channels but, as well, these embodiments insure that all exposed edges of the paperboard are protected. In other words, the prior art has recognized that when certain liquids are packaged in thermoplastic coated paperboard containers, such liquids may penetrate or wick into the paperboard at points where cut edges of the paperboard are exposed to the packaged liquid. Such wicking occurs because any such exposed, cut edge, for example the edges 46a, 46b, 49a and 48b of the gusset flaps and the edge 49 of the tuck-in flap, are uncoated. Referring to FIG. 2, it will be seen that, in prior constructions, ,both a portion of the edge 49 and the edge of the gusset flaps adjacent the gusset points were exposed to the packaged liquid and thus might wick. Similarly, if a penetrative liquid was packaged in a container having a bottom of the type shown in FIG. 2, the entire length of the edges associated with the gusset flaps and the tuck-in flap would be exposed to the packaged liquid as it flowed through the gusset channels and the tuck-in flap channel. As indicated above, the embodiments of the invention heretofore described not only seal or plug both the major leakage channels but, as well, protect all of the exposed edges of the paperboard. Thus, referring to FIG. 7, it will be seen that the exposed edges of the gusset flaps adjacent to the gusset points and the center portion of the edge 49 of the tuck-in flap 19a are covered and protected when the juxtaposed thermoplastic beads are melted. Additionally, the remainder portions of the juxtaposed beads plug at least the major leakage channels and therefore the remainder of the edges associated with the gusset flaps and the tuck-in flap are protected.

In the event that it is desired to package penetrative liquids and prevent leakage through the major leakage channels but protection of all exposed edges (i.e. uncoated edges) is not of primary concern, other embodi ments of our invention may be employed. To appreciate the nature of these other embodiments, attention is directed to FIGS. 8 and 9. Considering FIG. 8, it will be seen that the plugging or sealing of the channel 60 results from providing the juxtaposed beads of thermoplastic 92 adjacent to the channel and having a thickness of at least mils and preferably in the range of 10-12 mils. Thus, if a blank is employed which, when erected, provides a configuration of the type shown in FIG. 8, the major leakage channels will be sealed. Therefore, recognizing the importance of the configuration shown in FIG. 8, it has been determined that other blank constructions will provide this configuration. For example, the configuration may be obtained by providing a bead of thermoplastic material on only the tuck-in flap 19a and the cover flap 17a. A blank which would provide such a configuration would be a blank as shown in FIG. 10 wherein the beads 93 and 95 were omitted. Indeed, it has been found that the major leakage channels may be substantially sealed if a bead is provided upon only one of the major flaps, for example, the cover flap. If a bead is provided only upon the cover flap, it may be found to be desirable to position the bead such that, prior to melting, the bead is aligned with the channel 60 shown in FIG. 9 so as to promote the plugging of the channel when the bead melts.

Of course, it will be appreciated that if a bead of thermoplastic material is not provided upon each of the four bottom forming flaps, the thickness of the bead or beads which are provided must be greater than the 10-12 mil thickness previously recited, e.g. a thickness of approximatley 20 mils may be used.

Pursuing further the importance of the configuration shown in FIG. 8, it has been pointed out that the major leakage channel 60 is plugged by providing a thermoplastic bead or beads adjacent thereto. Thus, sealing of the major leakage channels will generally be achieved if one employs a blank having a narrow band of thermoplastic material disposed upon at least one of the bottom forming flaps so as to extend outward from both of the gusset points when a container is formed from the blank. The embodiments of our invention heretofore described provide this ultimate configuration although it may now be seen that still other blank constructions may be employed to provide the same ultimate configuration. For example, considering the blank of FIG. 6, a thermoplastic bead on corresponding portions of the two gusset flaps will provide the required ultimate configuration, e.g. a bead positioned adjacent to the edge 46a and a bead positioned adjacent to the edge 48a or a bead positioned on the edge 46b and a bead positioned on the edge 48b.

Although embodiments of our invention have been heretofore described with reference to a blank which, when erected, forms a square container, it will be appreciated that our invention is also applicable to blanks which, when erected, form rectangular containers. In the event that our invention is employed in combination with a blank which forms a rectangular container, the center portion of the tuck-in flap which would be exposed to the packaged liquid would be cut such that the length of this portion of the tuck-in flap would be equal to one half the width of the gusset forming flaps. In this manner, the tuck-in flap channel will be aligned with the gusset channels.

Similarly, our invention has hereinbefore been described with reference to embodiments wherein the sides of the thermoplastic beads are parallel, thus providing a bead of uniform width. However, the inner edge of the bead may be non-parallel with respect to the outer edge of the bead in order to provide a bead of varying width.

In summary, a number of embodiments of our invention have hereinbefore been disclosed and described. However, it will be appreciated that other embodiments may be apparent to those skilled in the art which are nevertheless within the scope of our invention as described in the claims appended hereto.

We claim:

1. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a heat sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points and gusset channels when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, and a tuck-in flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, the improvement which comprises;

a. the longitudinal length of at least the center portion of said tuck-in flap being approximately equal to one half the width of one of said gusset forming flaps and the remainder of said tuck-in flap disposed to entirely underlie said gusset forming flaps when said blank is erected; and

b. a narrow band of thermoplastic material disposed upon the interior side of at least one of said bottom forming flaps so as to extend outwardly from said gusset points and along said gusset channel when a container is formed from said blank, said band of thermoplastic material having a thickness of at least approximately 5 mils and a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said band being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap channel which is formed when said container is formed.

2. The blank of claim 1 wherein the longitudinal dimension of said band of thermoplastic material is at least approximately 0.125 inches.

3. The blank of claim 1 wherein said band of thermoplastic material is disposed upon said cover flap.

4. The paperboard blank of claim 3 wherein said band of thermoplastic material has a longitudinal dimension of at least approximately 0.125 inches.

5. The paperboard blank of claim 3 which further includes a band of thermoplastic material disposed upon said tuck-in flap.

6. The blank of claim 5 wherein said band of thermoplastic material has a longitudinal dimension of at least approximately 0.125 inches.

7. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a square head sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, said cover flap extending longitudinally beyond the transverse edges of said gusset forming flaps and a tuck-in flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, the improvement which comprises:

a. at least the center portion of the transverse edge of said tuck-in flap being substantially aligned with the transverse edges of said gusset forming flaps and the remainder of the edges of said tuck-in flap disposed to entirely underlie said gusset forming flaps when said blank is erected; and

b. a narrow band of thermoplastic material disposed upon the interior side of at least the center portion of each of said bottom forming flaps, the outer edge of all of said bands being substantially transversely aligned, the outer edge of said bands disposed upon said gusset forming flaps being adjacent to the exposed transverse edge of said gusset forming flaps and the transverse length of each of said narrow bands of thermoplastic material being sufficient to heat seal said gusset points and the center portion of the transverse edge of the tuck-in flap when said blank is formed and sealed, said bands of thermoplastic material having a thickness of at least approximately 5 mils and having a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said bands being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap channel which is formed when said container is formed.

8. The blank of claim 7 wherein said tuck-in flap is notched.

9. The blank of claim 8 wherein said narrow band or thermoplastic material is at least approximately 0.125 inches wide.

10. The blank of claim 8 wherein said notch is rectangular and the length of said band is at least equal to the transverse width of said notch.

11. The blank of claim 10 wherein said narrow thermoplastic band extends entirely across said blank.

12. The blank of claim 10 wherein the melt index of said thermoplastic is in the range of 3.0 to 300.

13. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a square heat sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points and gusset channels when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, said cover extending longitudinally beyond the transverse edges of said gusset flaps and a tuck-in flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, the improvement which comprises:

a. the transverse edge of said tuck-in flap being substantially aligned with the transverse edges of said gusset forming flaps with the outer transverse edges of the tuck-in flap underlying said gusset forming flaps when said blank is erected;

b. a narrow band of thermoplastic material disposed upon at least the center portion of each of said bottom flaps, all of said bands being substantially transversely aligned, the outer edge of said bands disposed upon said gusset forming flaps being adja-v cent to the exposed transverse edge of said gusset forming flaps and the transverse length of each of said narrow bands of thermoplastic material being sufficient to heat seal said gusset points and the center portion of the transverse edge of the tuck-in flap when said blank is formed and sealed, said band of thermoplastic material having a thickness of at least approximately 5 mils and a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said band being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap which is formed when said container is formed.

14. The blank of claim 13 wherein the width of said narrow band of thermoplastic material is at least, approximately, 0.125 inches.

15. The blank of claim 14 wherein said thermoplastic material has a melt index in the range of, approximately, 3.0 to 300.

16. The blank of claim 15 wherein said narrow band of thermoplastic material extends substantially across the entire blank. 

1. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a heat sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points and gusset channels when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, and a tuck-in flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, the improvement which comprises; a. the longitudinal length of at least the center portion of said tuck-in flap being approximately equal to one half the width of one of said gusset forming flaps and the remainder of said tuck-in flap disposed to entirely underlie said gusset forming flaps when said blank is erected; and b. a narrow band of thermoplastic material disposed upon the interior side of at least one of said bottom forming flaps so as to extend outwardly from said gusset points and along said gusset channel when a container is formed from said blank, said band of thermoplastic material having a thickness of at least approximately 5 mils and a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said band being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap channel which is formed when said container is formed.
 2. The blank of claim 1 wherein the longitudinal dimension of said band of thermoplastic material is at least approximately 0.125 inches.
 3. The blank of claim 1 whErein said band of thermoplastic material is disposed upon said cover flap.
 4. The paperboard blank of claim 3 wherein said band of thermoplastic material has a longitudinal dimension of at least approximately 0.125 inches.
 5. The paperboard blank of claim 3 which further includes a band of thermoplastic material disposed upon said tuck-in flap.
 6. The blank of claim 5 wherein said band of thermoplastic material has a longitudinal dimension of at least approximately 0.125 inches.
 7. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a square head sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, said cover flap extending longitudinally beyond the transverse edges of said gusset forming flaps and a tuck-in flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, the improvement which comprises: a. at least the center portion of the transverse edge of said tuck-in flap being substantially aligned with the transverse edges of said gusset forming flaps and the remainder of the edges of said tuck-in flap disposed to entirely underlie said gusset forming flaps when said blank is erected; and b. a narrow band of thermoplastic material disposed upon the interior side of at least the center portion of each of said bottom forming flaps, the outer edge of all of said bands being substantially transversely aligned, the outer edge of said bands disposed upon said gusset forming flaps being adjacent to the exposed transverse edge of said gusset forming flaps and the transverse length of each of said narrow bands of thermoplastic material being sufficient to heat seal said gusset points and the center portion of the transverse edge of the tuck-in flap when said blank is formed and sealed, said bands of thermoplastic material having a thickness of at least approximately 5 mils and having a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said bands being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap channel which is formed when said container is formed.
 8. The blank of claim 7 wherein said tuck-in flap is notched.
 9. The blank of claim 8 wherein said narrow band or thermoplastic material is at least approximately 0.125 inches wide.
 10. The blank of claim 8 wherein said notch is rectangular and the length of said band is at least equal to the transverse width of said notch.
 11. The blank of claim 10 wherein said narrow thermoplastic band extends entirely across said blank.
 12. The blank of claim 10 wherein the melt index of said thermoplastic is in the range of 3.0 to
 300. 13. In combination with a thermoplastic coated paperboard blank adapted to be erected to form a square heat sealed container, said blank having a body forming portion and a bottom forming portion, said bottom forming portion including two spaced apart gusset forming flaps having substantially aligned transverse edges and forming gusset points and gusset channels when said blank is erected, a cover flap foldably connected by a longitudinal fold line to at least one of said gusset forming flaps, said cover extending longitudinally beyond the transverse edges of said gusset flaps and a tuck-in flap foldably connected by a longitudinal fold line to at least onE of said gusset forming flaps, the improvement which comprises: a. the transverse edge of said tuck-in flap being substantially aligned with the transverse edges of said gusset forming flaps with the outer transverse edges of the tuck-in flap underlying said gusset forming flaps when said blank is erected; b. a narrow band of thermoplastic material disposed upon at least the center portion of each of said bottom flaps, all of said bands being substantially transversely aligned, the outer edge of said bands disposed upon said gusset forming flaps being adjacent to the exposed transverse edge of said gusset forming flaps and the transverse length of each of said narrow bands of thermoplastic material being sufficient to heat seal said gusset points and the center portion of the transverse edge of the tuck-in flap when said blank is formed and sealed, said band of thermoplastic material having a thickness of at least approximately 5 mils and a longitudinal dimension less than the longitudinal length of said bottom forming flaps, the thickness and area of said band being such that, when a container is formed from said blank and said thermoplastic material is melted, it will not cover the entire area defined by said bottom forming flaps, whereby, when said blank is formed into a container, said thermoplastic material will seal at least the center portion of said gusset channels and at least the center portion of the tuck-in flap which is formed when said container is formed.
 14. The blank of claim 13 wherein the width of said narrow band of thermoplastic material is at least, approximately, 0.125 inches.
 15. The blank of claim 14 wherein said thermoplastic material has a melt index in the range of, approximately, 3.0 to
 300. 16. The blank of claim 15 wherein said narrow band of thermoplastic material extends substantially across the entire blank. 